Recently in Teaching Category

Week 201: The Otic Ganglion

Ouch! That wasn't a nice way to start the second year of medical school was it?

OK, so most of the session was about the tongue and salivary glands, which seem simple enough until you start trying to hook them up. Then you get into cranial nerves and the intricacies of head and neck anatomy. How many cranial nerves does it take to work the tongue properly? And how on earth do those fibres get to those different parts of the tongue? Fun stuff.

I talked about the otic ganglion in far too much detail, so here is what you need to know:

The glossopharyngeal nerve (CN IX) sends a bundle of preganglionic parasympathetic nerve fibres across the floor of the middle cranial fossa and into the petrous part of the temporal bone.

Those fibres find their way through the middle ear and out of the skull into the infratemporal fossa.

Meanwhile, the third branch of the trigeminal nerve (CN V) known as the mandibular nerve (CN V3) drops through the foramen ovale to leave the skull and also enters the infratemporal fossa. It sends a branch of general sensory nerve fibres called the auriculotemporal nerve out towards the ear and the temporal region.

The otic ganglion is found beside the mandibular nerve inferior to the foramen ovale. The preganglionic parasympathetic nerve fibres from the glossopharyngeal nerve synapse here and postganglionic parasympathetic nerve fibres pass with the auriculotemporal nerve out to the parotid salivary gland. They will convey secretomotor signals to cause the parotid gland to secrete saliva.

Got it?

I also mentioned the other parasympathetic ganglia of the head: the ciliary ganglion, pterygopalatine ganglion and submandibular ganglion. We talked about their associated cranial nerves, but you've met some of them and will meet them again.

The other point of note was that sympathetic nerve fibres pass up into the head by following the major arteries, and sympathetic fibres jump from the middle meningeal artery (passing through the foramen spinosum and therefore really close to the foramen ovale and the otic ganglion) to the otic ganglion and also pass with the auriculotemporal nerve to the parotid gland. Probably. Mostly. These fibres have vasoconstrictive effects. The sympathetic fibres are already postganglionic, and do not synapse in the otic ganglion.

Links

Want to review your cranial foramina (and bone and suture) knowledge? Check out my interactive skull.

Above image from: commons.wikimedia.org/wiki/File:Gray783.png

Teaching

I've given a couple of lectures over the last couple of weeks on the first 18 days of development and the embryology of the cardiovascular system. If you're a Swansea student looking for my blog notes go back to Blackboard and you'll be able to download the whole lecture plus the other stuff I linked to.

If you're a non-Swansea student go on to my Medicine page and grab the podcasts. They cover the same content as the lecture, more or less. More, probably.

Neuroscience podcast 4: autonomic nervous system

Phil & I recorded another neuroscience podcast. Number 4 covers the autonomic nervous system and we talk about the anatomy, the wiring of the neurones, and the neurotransmitters involved.

I might have to listen to that neurotransmitters section a few more times.

MP3: Neuroscience podcast 4 - autonomic nervous system.

iTunes: Neuroscience podcast 4 - autonomic nervous system (enhanced format).

Anatomy & embryology podcast 24

OK, I finally finished the latest podcast in which Rhiannon and I talk about what we think are the important aspects of the anatomy of the lower limb. This is the first part of two, and is 45 minutes long. We talk about the bones of the foot and ankle, the knee, the sciatic nerve, veins, and compartments of the leg. We've got another 5 topics to talk about in episode 25.

Get it from iTunes or from the Medicine page. The iTunes enhanced version has a bunch of images in it.

Learning

Here's a great blog entry about learning for educators and lurners alike:

Donald Clark Plan B: 10 techniques to massively increase retention

There's a lot of really good stuff in there, hopefully stuff we're already trying to do in Swansea. Note number 9: mobile technology. The author talks about drip feeding assessment via those mobile devices that we all have in our pockets. Hopefully some of you have noticed that I've been coincidentally trying to do exactly this using the medium of the moment: Twitter.

Twitter pretty much started with mobile devices (you could use the internet and SMS text messages to post tweets really easily). Can yours follow twitter? If you have a mobile browser on your phone then, yes. Otherwise see this twitter mobile phone FAQ (although that's a little bit retro).

Follow me @samuelwebster and keep your eyes on the twitterwall (which is also linked to from the elearning section of the Swansea Blackboard).

I'll be drip feeding questions that you should be able to answer. You know, the sort of stuff that comes up in exams.

Anatomy: the lumbosacral plexus and the lower limb

On Monday we started looking at the structure of the hip, the muscles there and the nerves involved in motor and sensory innervation. In my station we talked about the lumbosacral plexus. Lots of nerves!

A nerve plexus is merely a lot of separate nerves (it's probably best to think of long, individual nerve cells) coming together into a group and then separating off towards different destinations. Some nerves from different spinal roots run off to those destinations together. It's like cabling in a building. There are no connections between nerves in a plexus.

We said that the lumbar plexus + sacral plexus = lumbosacral plexus. You may read that the coccygeal plexus is involved too, and yes, the coccygeal nerve (the last pair of spinal nerves!) links with sacral nerves.

[Need to review the spinal cord? Check here (missing coccygeal nerve) and here].

The roots of the lumbar plexus are formed by spinal nerves L1-L4. Remember that the posterior rami pass to the back muscles, so the lumbar plexus is formed from anterior rami. The lumbar plexus lies deep to and within the psoas muscles, and the nerves will pass on to the lower limb and the lower part of the abdomen.

The nerves L4 and L5 come together to form the lumbosacral trunk. This links to the sacral plexus, joining the two plexuses and making it easier for us to take them together as the lumbosacral plexus.

The sacral plexus forms from the spinal nerves S1-S5 an lies upon the piriformis muscle. The major nerve from the sacral plexus is the pudendal nerve (S2-S4, main sensory nerve for external genitalia and motor to muscles of continence including the external urethral and anal sphincters and levator ani - these also receive other motor innervation though). The sacral plexus also forms many tiny, short nerves that directly innervate the muscles of the hip that the plexus lies on or near. As such these nerves may be difficult to identify but they exist, for example, the nerve to obturator internus (and gamellus superior) and the nerve to quadratus femoris (and gamellus inferior). Confusing? Sorry.

The nerves of the lumbosacral trunk are combined with the sacral plexus to form the sciatic nerve (L4-S3). This giant nerve running out through the greater sciatic foramen and into the gluteal region descends the length of the posterior lower limb, innervating the posterior compartment of the thigh and all the muscles distal to the knee. It splits into tibial and common fibular (or peroneal) nerves before it reaches the popliteal region behind the knee. This monster nerve, along with the superior gluteal nerve (L4-S1) and inferior gluteal nerve (L5-S2) is the reason why we consider the lumbar and sacral plexuses together. The number of spinal nerves contributing to the sciatic nerve (and the lumbar location of those roots) suggest that it is more likely to suffer impingement than any other nerves. I'm sure that most of you will be aware of sciatica. As the sciatic nerve passes into the gluteal region and is very large you must be aware of its location if you're considering sticking needles into someone's bum.

We didn't talk about the parasympathetic nerves arising within the pelvis, so we'll pick those up in other, pelvic-related weeks. The pudendal nerve also takes a very interesting route to reach its destination outside the pelvis, which we'll also discuss in other sessions.

So, the lumbosacral plexus is formed from the anterior rami of spinal nerves L1-S5. The most important nerves to watch out for are probably those mentioned above, the lumbosacral trunk is the link, and the sciatic nerve (and gluteal nerves) is the main reason for the link. Make sure you can link these plexuses and nerves into your understanding of the abdomen, pelvis and lower limb.

Higher Education Academy mag & Turning Point clickers

I've been a proponent of using interactive feedback technology in lectures (which means I can ask questions in my lecture, students can answer using a remote control with 10 or so buttons on it and we can all see how well we're doing) for some time. As such I've been occasionally pulled out to demonstrate the tech and to get other people using it.

I've written a couple of brief things about how we've been using this in embryology lectures in the School of Medicine and the Higher Education Academy's magazine "01" has included an article in this quarter's copy.

The students like it and the lecturers like it. Everybody likes to use the clickers (instant gameshow) and teachers get to see immediately how much the audience is getting from the lecture. It's simple to use and as more people have used it more Schools have bought their own sets. I imagine that in modules with very large student numbers if you can afford enough clickers you'll learn a lot about your audience. Is it possible to interact with every individual in a lecture with 300 students in an hour in any other way?

For more information:

- see the HEA 01 article here (HTML) or here (pdf)
- visit Turning Technologies to find out more about the tech

Neuroscience podcast no. 3 - Neurotransmitters

Phil tried really hard to teach me about neurotransmitters in our most recent podcast. We talked about how they work and went through a list of the key neurotransmitters and gave an overview of what they do. Many of them will be talked about in more detail in future podcasts!

My poor brain.

MP3: Neuroscience podcast - No.3 Neurotransmitters.

iTunes: Neuroscience podcast - No.3 Neurotransmitters (iTunes).

Anatomy: the orbit & superior orbital fissure

On Monday we went through the bones of the orbit, what the superior orbital fissure (and inferior orbital fissure and optic canal) were, and what went through it (and them).

To review the bones of the orbit look at these images. Hover over the bones to be reminded of their names. We also noted that the palatine bones just about reach up to the orbit, but you can't see this on the images.

The superior orbital fissure is the slit in the posterior wall of the orbit. It passes through to the middle cranial fossa within the cranial cavity. The inferior orbital fissure is the slit in the floor of the orbit passing to the infratemporal fossa.

The superior orbital fissure is the main route for stuff to get from the brain to the orbit then. Everything in the orbit (muscles, glands, mucosa, skin, etc) will need to receive nerve fibres from cranial nerves passing through the superior orbital fissure. The optic nerve and the retina are the exceptions to this.

With regards to blood supply though, the ophthalmic artery passes through the optic canal with the optic nerve. It is a branch from the internal carotid artery and sends arterial branches out and around the orbit. The ophthalmic veins (there are superior and inferior opthalmic veins) do pass through the orbital fissures. Maybe a little counterintuitively the superior ophthalmic vein drains blood from the orbit back into the cranial cavity by passing through the superior orbital fissure. (The venous blood passes to the cavernous sinus on the other side and eventually leaves the cranial cavity through the internal jugular vein). This gives a route by which infection or drugs can pass intracranially from superficial structures, and will no doubt be mentioned a number of times in your studies. The inferior opthalmic vein connects to the pterygoid venous plexus of the face by sending branches through the inferior orbital fissure.

So what nerves pass through the superior orbital fissure? In essence, cranial nerves III, IV, V and VI. Easy, eh? Well, there's a little more detail to it that you need to know.

CN III
Also known as the oculomotor nerve, this sends fibres to almost all of the muscles in the orbit (both extra-ocular and intra-ocular, i.e. the muscles of the lense and the constrictor muscle of the iris). It divides into superior and inferior branches before it emerges from the superior orbital fissure.

CN IV
Also known as the trochlear nerve (trochlea comes from the Greek word for "pulley", and this is the nerve to a muscle that has a pulley) this is another motor nerve with the singular task of innervating the superior oblique muscle.

CN V
Here things get a little more complicated. Cranial nerve V is the trigeminal nerve, which divides into 3 branches within the cranial cavity: V₁ (ophthalmic nerve), V₂ (maxillary nerve) and V₃ (mandibular nerve). These are the sensory nerves of the face (although you'll remember that the mandibular nerve also sends some motor fibres to the muscles of mastication) and we're interested in the ophthalmic nerve when we look at the orbit. Just before the ophthalmic nerve enters the superior orbital fissure it divides into 3 smaller nerves:
- frontal branch
- lacrimal branch
- nasociliary branch

So that's a little inconvenient and tricky to remember. Note that some of these branches are rather interesting in function and in the other nerve fibres that they pick up that are not from the trigeminal nerve, but I won't talk about that here.

CN VI
Last of all we have the abducent nerve (or abducens, whichever you prefer). The name of this nerve comes from its ability to abduct the eye, as it sends motor fibres to the lateral rectus muscle.

That's about it for structures passing through the superior orbital fissure. Make sure that you can link all this up with what you learnt about the other parts of the orbit and the eye, and what you will learn about the functions of those structures.

Neuroscience podcast no. 2

Another neuroscience podcast is out: Phil tells me why my weight is fairly stable, what happens in my brain when I get hungry and what changes when I have eaten. We talk about the adipostat, leptin, ghrelin and obesity, why we choose particular foods and how dopamine, opioids and (probably) serotonin are involved.

MP3: Neuroscience podcast - No.2 Neurobiology of appetite regulation.

iTunes: Neuroscience podcast - No.2 Neurobiology of appetite regulation (iTunes).

X-ray at 18 days.

For interest. This oblique view is more telling than the A-P.

New neuroscience podcast!

Phil Newton (henceforth to be known as Dr Phil) and I have begun a new podcast series to help medical students and others in similar need learn about neuroscience. Phil intends the series to be complementary to the lecture series in Swansea, but it should be useful and maybe even interesting to students anywhere.

In the first episode Dr Phil teaches me about action potentials and how neurons signal other neurons. Its about 35 minutes long and you can subscribe to the podcast in iTunes or download the MP3s from this blog or Dr Phil's.

MP3: Neuroscience podcast - No.1 Action potentials and synapses.

iTunes: Neuroscience podcast - No.1 Action potentials and synapses (iTunes).

Podcast episode 23

A new podcast is up on iTunes and the medicine page of my blog. Rhi and I finish talking about our list of things med students really should know about the anatomy of the pelvis. We include the vas deferens and the urethra, the os, the organs of the female pelvis and their ligaments, and sensory innervation from external genitalia.

Links:

- Subscribe in iTunes

- Download the MP3: Episode 23: 10 things you should know about the anatomy of the pelvis (part 2).

Week 121: Skull, the temporal region

This week we made it all the way up to the head. To look at the anatomy of the head, we need to start by looking at the bones. Different stations looked at different parts of the skull and teeth, and I spoke about the temporal region.

The temporal region (or as laymen may call it, your "temples") lies superior to the zygomatic arch and within the edges of the temporalis muscle. You may see curves on the skull around the edge of the temporal fossa that correspond to the attachment of the flat temporalis muscle. There is a depression here in which a few superficial structures lie, and this is the temporal fossa.

The bones here are the parietal bone, the temporal bone (it has squamous - flattened - and petrous - lumpy/rocky - parts) and the sphenoid bone. Use the skull bone images here to see these. Note also the frontal bone and the zygomatic bone. Spend some time in the lab with a coloured skull and a detailed skull (the numbered ones are best) to be clear on the shapes of these bones.

We talked about the nature of sutures linking the bones of the skull, which are fixed in the adult and contribute to the aim of the skull to protect the brain. There are some sutures that you should be able to name and you can also see these in the skull images (here). Note also the bregma (where the coronal suture meets the sagittal suture) and the lambda (where the sagittal suture meets the lambdoid suture).

These points correspond to where the anterior and posterior fontanelles were at birth. The bones of the skull are able to slide over one another to some extent to aid passage through the birth canal, and this is known as moulding. The bones are not fixed by sutures at this time, but are linked by softer membrane-like connective tissues. After birth the anterior fontanelle is known as the soft spot and can be an important diagnostic indicator. The fontanelles also allow the bones of the skull to grow.

Back to the temporal region: the sutures linking the parietal, frontal, sphenoid, and temporal (squamous) bones join here to form an H-shaped group of sutures known as the pterion. This potential weakness in the skull is made weaker by a thinning of the bones here (you can often see this on real skulls in the lab, but not on plastic skulls). To make matters even worse, the middle meningeal artery runs inside the skull, deep to the pterion. A fracture here is likely to tear the middle meningeal artery, causing blood to pool between the bone and the dura mater, pressing on the brain. This is an extradural haemorrhage and can be fatal (and in fact, dural venous sinuses may also be involved).

The temporal fossa has a few superficial structures of interest passing through it. The pulse you feel in your "temples" is the pulse of the superficial temporal artery, a branch from the end of the external carotid artery. The superficial temporal vein, draining a similar area of the scalp, is nearby. The superficial nerve here is the auriculotemporal nerve. This nerve carries sensory information from this area, and is a branch of the mandibular nerve, which itself is a branch of the trigeminal nerve, also known as cranial nerve V (CN V). I have a feeling we will be meeting this nerve again in the future when we start adding more detail to our head and neck anatomy and look at the infratemporal fossa. For example, this nerve also carries parasympathetic nerve fibres from CN IX to the parotid gland (that tell it to secrete saliva).

Fun, eh? The anatomy of the head and neck can be very detailed, delicate and intricate. It's a fascinating region anatomically, and by building up your knowledge bit by bit over the next 18 months or so you should develop a solid understanding of what's going on in there.

Elearning: skull bones

We're looking at some head and neck anatomy on Monday, and some stations will be looking at the bones of the skull. I have an elearning thingy here to help you with bones, sutures and foramina of the head:

www.dontbeasalmon.net/elearning/skull